This invention relates in general to a voltage and current sensing apparatus with a cast resin body which measures both voltage and current in a conductor at a potential greater than 15 Kilovolts. As the voltage of a conductor increases, corona effects or partial discharges in associated insulative media become more difficult to avoid. If they are not avoided, shortened equipment life, and audio and radio frequency noise pollution can result. It is also necessary to avoid galvanic corrosion among components of the line sensor and the conductor. In particular, the invention relates to a voltage and current sensor transducer support apparatus containing an interior coil having a non-magnetic core, a non-inductive resistance voltage divider, and a corona shield. In addition to sensing the power parameters of current and voltage in the conductor, the transducer support positions and holds up the conductor.
Current and voltage sensors are generally used by utility companies to electronically control capacitor banks, voltage regulators, reclosures, switches, electrical distribution, feeder optimization, and for conservation, load managing, and remote metering. Prior art devices, while accomplishing these feats, do not produce repeatable, consistent readings. This is primarily due to the fact that the prior art devices utilize an iron core transformer coil.
Present devices for indicating or sensing voltages or currents of conductors of power lines for purposes of metering or control are relatively complex, difficult to connect with the conductors of the power line and often cannot be connected with the power line conductors unless time consuming safety procedures and safety devices are employed. With most prior art voltage and sensing devices, the power line must be disconnected so as to stop the flow of electricity therethrough and, in many applications, the power line must be cut to allow the insertion of the current sensing apparatus. This requires down time and loss of revenue to the utility company.
It is generally known that coil output is affected by the outside diameter of the primary cable. Prior art sensing apparatus have used charts and graphs to approximate the voltage and current sensing information developed from the iron core transformer coil. This use of charts and graphs has been cumbersome and difficult to generate or even apply with varying cable sizes. This has produced non-repeatable results with respect to voltage and current sensors. In a utility application, approximately 200 different cable sizes could be used between 0.25 inch in cable diameter through 1.25 inches cable diameter. In view of these varying cable sizes, it is difficult to generate or even apply individual correction factors to each cable size. This is particularly true where an iron core coil has been used. As the voltage and current levels increase, the iron core saturates and will not produce consistent readings. Thus, companies, in the past, manufacturing voltage and current sensors have used a graph which does not progress in a linear fashion.
A combined current and voltage measuring apparatus is shown in U.S. Pat. No. 4,074,193 to Kohler, entitled COMBINED CURRENT AND VOLTAGE MEASURING APPARATUS. Another voltage or current sensing apparatus is shown in U.S. Pat. No. 3,251,014 to Stein, Jr., entitled ELECTRICAL COUPLING DEVICE. These patents are illustrative of the prior art with respect to voltage and current sensing apparatus used in high voltage applications. The patent to Kohler illustrates one version of a sensing apparatus that requires the power through the conductor be discontinued for installation of the sensor.
Generally, current and voltage sensing apparatus which do not require the disconnection of the primary conductor, such as the one shown in U.S. Pat. No. 3,251,014, to Stein, Jr., entitled ELECTRICAL COUPLING DEVICE, utilize an iron core coil. Use of the iron core coil will produce a non-linear and generally non-repeatable response with respect to voltage or current deviations or applications, and thus renders such devices relatively inaccurate for various applications. Further, the Stein, Jr. reference does not disclose any means for mechanically maintaining the conductor in the groove at the top of the casting. Thus, the Stein reference does not teach a means by which the conductor is positioned with respect to the groove. Positioning of the conductor in a voltage and current sensing apparatus is critical for obtaining precise and repeatable readings from the sensing apparatus.
Capacitively graded bushings to reduce voltage stresses are generally known. An patented example of such is provided by U.S. Pat. No. 3,770,877 issued to Mashikian et. al. on Nov. 6, 1973 describing a CAPACITIVELY GRADED ELECTRICAL INSULATING DEVICES. U.S. Pat. No. 3,418,575 issued to Spindle on Dec. 24, 1968 describing a HIGH VOLTAGE CURRENT MEASURING DEVICE EMPLOYING MEANS RESPONSIVE TO THE ELECTROMAGNETIC FIELD GENERATED BY THE CURRENT includes a plurality of capacitor plates, one of which is circular and caps the insulative reservoir. Shields are also shown in connection with current sensors such as U.S. Pat. No. 3,380,009 issued to Miller on Apr. 23, 1968 describing a HIGH VOLTAGE CURRENT TRANSFORMER, and U.S. Pat. No. 3,456,222 issued to Berg on Jul. 15, 1969 describing a HIGH VOLTAGE CURRENT TRANSFORMER.
It is, therefore, an object of the present invention to provide a voltage and sensing apparatus which allows installation without interference with the primary conductor and without disconnecting the power supply through the conductor. Further, it is an object of the invention to provide a voltage and sensing apparatus which securely maintains the primary conductor precisely adjacent a select portion of the sensing apparatus for purposes of producing an even and measured response with respect to the metering and measuring of current and voltage.
It is another object of the present invention to provide a voltage and current sensing apparatus which produces a linear and repeatable response in all applications with respect to varying currents, voltages and conductor diameters.
It is a further object of the present invention to provide a voltage and current sensor which may replace an existing insulator on a power line and thus provide the mechanical support to the conductor which was previously supplied by the insulator. It is another object of the present invention to provide a design that can replace existing monitoring type sensing devices with considerable reduction of costs. It is another object of the present invention to provide a sensing device that can be installed without disrupting service to a customer and without modifications to the utility pole structure. It is a further object of the present invention to provide a sensor which will provide a linear output proportional to the current and voltage on the line which can then be input into a transducer to allow communication with a utility company computer network. These goals must be attained without corona or partial discharges in or around the line sensor, or galvanic corrosion among components of the line sensor and the conductors.